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bq2022A

SLUS724E – SEPTEMBER 2006 – REVISED MARCH 2016

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Programming (continued)

7.5.5 READ MEMORY Commands

Two READ MEMORY commands are available on the bq2022A. Both commands are used to read data from the

1024-bit EPROM data field. They are the READ MEMORY/Page CRC and the READ MEMORY/Field CRC

commands. The READ MEMORY/Page CRC generates CRC at the end any 32-byte page boundary whereas

the READ MEMORY/Field CRC generates CRC when the end of the 1024-bit data memory is reached.

7.5.5.1 READ MEMORY/Page CRC

To read memory and generate the CRC at the 32-byte page boundaries of the bq2022A, the SKIP ROM

command is followed by the READ MEMORY/Generate CRC command, C3h, followed by the address low byte

and then the address high byte.

An 8-bit CRC of the command byte and address bytes is computed by the bq2022A and read back by the host to

confirm that the correct command word and starting address were received. If the CRC read by the host is

incorrect, a reset pulse must be issued and the entire sequence must be repeated. If the CRC received by the

host is correct, the host issues read time slots and receives data from the bq2022A starting at the initial address

and continuing until the end of a 32-byte page is reached. At that point, the host sends eight additional read time

slots and receive an 8-bit CRC that is the result of shifting into the CRC generator all of the data bytes from the

initial starting byte to the last byte of the current page. Once the 8-bit CRC has been received, data is again read

from the 1024-bit EPROM data field starting at the next page. This sequence continues until the final page and

its accompanying CRC are read by the host. Thus each page of data can be considered to be 33 bytes long, the

32 bytes of user-programmed EPROM data and an 8-bit CRC that gets generated automatically at the end of

each page.

Initialization and SKIP

ROM Command

Sequence

READ

MEMORY/Generate

CRC Command

Address Low Byte

Address High

Byte

Read and

Verify CRC

EPROM Memory and

CRC Byte

Generated at 32-Byte

Page

Boundaries

C3h

A0

A7 A8

A15

NOTE: Individual bytes of address and data are transmitted LSB first.

Figure 7. READ MEMORY/Page CRC

7.5.5.2 READ MEMORY/Field CRC

To read memory without CRC generation on 32-byte page boundaries, the SKIP ROM command is followed by

the READ MEMORY command, F0h, followed by the address low byte and then the address high byte.

NOTE

As shown in Figure 8, individual bytes of address and data are transmitted LSB first.

An 8-bit CRC of the command byte and address bytes is computed by the bq2022A and read back by the host to

confirm that the correct command word and starting address were received. If the CRC read by the host is

incorrect, a reset pulse must be issued and the entire sequence must be repeated. If the CRC received by the

host is correct, the host issues read time slots and receives data from the bq2022A starting at the initial address

and continuing until the end of the 1024-bit data field is reached or until a reset pulse is issued. If reading occurs

through the end of memory space, the host may issue eight additional read time slots and the bq2022A responds

with an 8-bit CRC of all data bytes read from the initial starting byte through the last byte of memory. After the

CRC is received by the host, any subsequent read time slots appear as logical 1s until a reset pulse is issued.

Any reads ended by a reset pulse prior to reaching the end of memory does not have the 8-bit CRC available.